This invention relates to an electronic musical instrument, and more particularly an electronic musical instrument of the type for sequentially calculating a plurality of partial tone signals with a plurality of time divisioned time slots such that these partial tone signals are synthesized to form a musical tone signal.
A partial tone synthesizing system disclosed in U.S. Pat. Nos. 3,809,786 and 3,809,788 both issued May 7, 1974 is known as one example of an electronic musical instrument in which a plurality of partial tone components (higher harmonic components are sequentially calculated in a plurality of time divisioned time slots and the calculated partial tone components are synthesized for the purpose of forming a musical tone.
Since in the electronic musical instrument of such partial tone synthesizing system, a plurality of time divisioned time slots of the number equal to the number of the partial tone signals to be synthesized are provided and since in each time divisioned time slot only one preassigned partial tone signal is calculated, it is necessary to provide the time divisioned time slots of the same number as that of the partial tone signals to be synthesized with the result that where a musical tone producing signal containing a plurality of partial tone signals is to be formed, the number of the time divisioned time slots is increased thus increasing the size of the circuit.
As a consequence, as disclosed in Japanese Preliminary Publication of patent No. 32028 of 1980 (corresponding to U.S. Ser. No. 067,693), an electronic musical instrument has been proposed in which a window signal of a predetermined time such as a Hanning window signal is multiplied with a partial tone signal of a predetermined frequency, for example a sine wave signal, for simultaneously calculating a plurality partial tone signals in a predetermined frequency bandwidth having the frequency of a predetermined partial tone signal at the center.
Since this electronic musical instrument is constructed such that a waveform obtained by amplitude modulating a predetermined partial tone signal with a Hanning window signal is prestored in a memory device and the stored waveform is read out by an address signal having a period corresponding to the time width of the Hanning window signal, the relation between the Hanning signal and the predetermined partial tone signal would be fixed so that there is a disadvantage that it is impossible to arbitrarily set the frequency bandwidth of a plurality of partial tone signals which are calculated simultaneously.
To obviate this disadvantage one may consider a system in which different amplitude modulated waveforms are stored in a plurality of memory devices so as to selectively read out any desired waveform. With this system, however, the number of the memory devices increases, thus increasing the size of the apparatus.